The present invention relates to an offset printing method using an image recording element, which specifically comprises a conductive transparent base plate, a photoconductive layer, a layer composed of an electrochromic material, and a conductive transparent electrode.
One display device utilizing a reversible oxidation-reduction color reaction of electrochromic material is disclosed in U.S. Pat. No. 3,736,034 hereby incorporated by reference. The principle of operation of electrochromic material in the aforesaid publication will be explained in reference to the drawings.
In FIG. 1, an electrochromic material 3 sandwiched between two electrodes 1 and 2 is transparent when switch 4 is open while it is colored on the side of cathode when the switch 4 is closed. The reference numeral 5 designates a transparent base plate, 6 a spacer and 7 a bias power source.
FIG. 2 shows a display cell in which, for example, an aqueous solution of benzylbiorogenchloride is sandwiched between two sheets of glasses. One glass is internally provided with a common electrode 8, and the other is provided with a number of display electrodes 9. When negative voltage of -1V with respect to the common electrode 8 is applied to the display electrodes 9, electrons cause biorogen ion on the display electrodes to be colored in blue. This blue coloring matter is insoluble in water and forms a thin layer of coloring matter on the surface of the display electrodes 9. The numeral 10 is a wiring to the display electrodes 9.
Representative of a reaction formula as utilized in the instant invention is given in the following: ##STR1## R may be CH.sub.3 (CH.sub.2).sub.5, CH.sub.3 (CH.sub.2).sub.6 or C.sub.6 H.sub.5 CH.sub.2
In this case, even if the voltage is removed, the layer of blue-purple coloring matter remains on the electrode to exhibit memory characteristics. This image may be erased by application of voltage opposite in polarity between the display electrodes or by short-circuiting between the electrode. That is, the biorogen ions emit electrons to the display electrodes and returns to its initial colorless state causing the blue-purple color to disappear.
The conventional operating process of the display element using the electrochromic material has been discussed, but this method suffers from the following drawbacks. Since the electrodes are used for the purpose of display, the images to be displayed are determined depending upon the shape of display electrodes, and hence, other shapes are not possible. This method further poses a disadvantage such that input entered is in the form of an electric signal, and therefore, where light is desired to be used as input, direct input is impossible.
Lithographic printing is a well-known and established art. In general, the process involves printing from a flat plate, relying upon the existence of different properties in the image and non-image areas for printability. In conventional lithography, the non-image area is hydrophilic while the image area is hydrophobic. In the lithographic printing process of a fountain solution is applied to the plate surface which wets all portions of the surface not covered by the hydrophobic image. This solution keeps the plate moist and prevents it from scumming up. An oil based printing ink is applied to the image bearing surface deposting the lithographic ink only on the image area, the hydrophilic wetted non-image area repelling the ink. The ink image may then be transferred directly to a paper sheet or other receptive surface, but generally it is transferred to a rubber offset blanket which in turn transfers the print to the final copy sheet. Hence, for each print made during a run, a lithographic plate is first dampened with an aqueous fountain solution, inked with a lithographic ink and finally printed either directly or by offset techniques.
A number of techniques are known for preparing lithographic printing plates. In a majority of instances, the substrate material upon which the oleophilic image is developed is itself hydrophobic and requires the application of secondary solutions referred to as conversion solutions which render the background, non-image areas hydrophilic. Therefore, while basically the presently known systems have been found to be useful for lithographic purposes, there are existing inherent disadvantages to their use.
When printing with the conventional lithographic printing plates it is difficult to determine the quality of the printing master other than by copy formation. The image and nonimage areas are substantially the same color and visual inspection does not reveal any meaningful differences. Further, it may be difficult to determine that the cause of a poor quality print is the master and not failures in the operation of other components of the printing process. Therefore, it would be of advantage to have a method of forming printing masters which could be easily visually inspected for defects.
In the formation of displays by the above described method of U.S. Pat. No. 3,736,043, it is necessary that electrodes be placed so as to allow image reproduction. This limits the images formed to those areas and shapes served by previously constructed controls and shapes.
It is, therefore, an object of this invention to overcome the above noted disadvantages of previous systems.
It is a further object to form printing masters which may be easily visually inspected.
It is an additional object to form electrochromic images from light images.
It is another object to form clear offset printed images.
It is a further object to form clear, sharp display images.
It is again an object of this invention to form a printing master that may be easily erased.
It is again another object of this invention to form a colored printing master.